1. Field of the Invention
The present invention relates to touch panels to be used primarily for operating various electronic equipment.
2. Background Art
In recent years, advance in multifunctionality and diversification of various electronic equipment such as mobile phones, car navigation systems or the like has been seen. Along with this trend, there has been an increase in electronic equipment in which various functions can be switched by pushing with a finger or a pen an optically transparent touch panel provided on the front surface of a display device such as a liquid crystal display while visually identifying through the touch panel what is displayed on the display behind the touch panel. Accordingly, touch panels are being sought that have good visibility and which assure precise operation.
Referring to FIGS. 4 through 6, description will now be given of a conventional touch panel. For easy understanding of the construction, the drawings are partially enlarged.
FIG. 4 is a sectional drawing of a conventional touch panel. FIG. 5 is a plan view of the upper board and the wiring board of FIG. 4. FIG. 6 is a plan view of the lower board and the wiring board of FIG. 4. In FIG. 4, upper board 1 and lower board 2 are films or thin sheets and are optically transparent. On the rear face of upper board 1 is formed optically transparent upper conductive layer 3 made of indium tin oxide. On the top face of lower board 2 is formed optically transparent lower conductive layer 4 made of indium tin oxide.
As shown in FIG. 5, a pair of upper electrodes 5, 6 made of silver and the like is formed on the top and bottom edges of upper conductive layer 3. Upper electrodes 5, 6 extend along the outer periphery of upper conductive layer 3, and plural leads 5A, 6A are provided on upper conductive layer 3. Also, as shown in FIG. 6, a pair of lower electrodes 7, 8 is provided at the left and right edges of lower conductive layer 4. Lower electrodes 7, 8 extend along the outer periphery of lower conductive layer 4, and plural leads 7A, 7B are provided at edges of lower conductive layer 4.
Also, as shown in FIG. 5, dummy pattern 9A and plural dummy patterns 9B are formed on the lower edge of upper board 1, and dummy pattern 9C is provided at the right edge in order to keep parallelism between upper board 1 and lower board 2. Slits 10A, 10B, 10C are formed at the inner right of upper electrode 5 of upper board 1, between upper electrodes 5, 6, between leads 5A, 5B, between leads 5A, 6A, at inner left of dummy pattern 9C, and between upper electrode 6 and dummy pattern 9A, by removing upper conductive layer 3 by means of laser processing and the like.
Also, as shown in FIG. 6, dummy pattern 9D is provided on the upper edge of lower board 2 and plural dummy patterns 9E are provided on the bottom edge in order to keep parallelism between upper board 1 and lower board 2. Slits 10D, 10E are formed at the inner top of lower electrodes 7, 8 of lower board 2, between leads 7A, 7B, and at the inner bottom of dummy pattern 9D, by removing lower conductive layer 4 by means of laser processing and the like. With these slits, short-circuiting between each electrode and the dummy patterns can be prevented thus maintaining insulation.
Also, plural dot spacers (not shown) are formed with an insulating resin at a predetermined interval on the top face of lower conductive layer 4. Nearly-frame-shaped spacer 11 is provided on the outer periphery on the top face of lower board 2, and outer peripheries of upper board 1 and lower board 2 are glued together with adhesive layer 12 coated on the top face of spacer 11. Upper conductive layer 3 and lower conductive layer 4 are oppositely disposed with a predetermined gap in between.
Furthermore, filmy wiring board 13 is sandwiched between upper board 1 and lower board 2. Upper edges of plural wiring patterns 14, 15 formed on the top and bottom faces of wiring board 13 are bonded and connected with leads 5A, 6A, leads 7A, 8A, respectively, with an anisotropic conductive adhesive (not shown) thereby completing a touch panel. Here, the anisotropic conductive adhesive is manufactured by dispersing conductive particles in a synthetic resin.
A touch panel constructed in this way is disposed on a front face of a display device such as a liquid crystal display and mounted on electronic equipment. And, plural wiring patterns 14, 15 of wiring board 13 are connected to electronic circuits (not shown) of the electronic equipment with a connector or by soldering.
In the above configuration, by pressing top face of upper board 1 with a finger or a pen in accordance with what is displayed on the display device behind the touch panel, upper board 1 is warped making upper conductive layer 3 of the pressed location come in contact with lower conductive layer 4. Subsequently, a voltage is sequentially applied from the electronic circuit through plural wiring patterns 14, 15 of wiring board 13 to both edges of upper electrodes 5, 6 and lower electrodes 7, 8 and to both edges of lower conductive layer 4 which is in an orthogonal direction. The electronic circuit detects the pressed location based on the ratio of these voltages, and switching of various functions of the electronic equipment is enabled.
That is, under a condition in which plural menus are displayed on the display device behind the touch panel, when the top face of upper board 1 on top of a desired menu is pressed, the electronic circuit detects the pressed location through plural wiring patterns 14, 15 of wiring board 13. In this way, selection of a desired menu from among plural menus can be made.
In such a touch panel, plural dummy patterns are formed in order to maintain parallelism between upper board 1 and lower board 2 in addition to upper electrodes 5, 6 and lower electrodes 7, 8. In addition, in order to prevent short-circuiting between electrodes and dummy patterns and maintain insulation, gap 17A is provided between upper right edge of upper electrode 5 of upper board 1 and upper edge of dummy pattern 9C, and gap 17B is provided between lower edge of dummy pattern 9C and right edge of dummy pattern 9A, for example.
Similarly, gap 17C is provided between upper edge of lower electrode 7 of lower board 2 and left edge of dummy pattern 9D, and gap 17D is provided between right edge of dummy pattern 9D and upper edge of lower electrode 8. Nearly-frame-shaped spacer 11 and adhesive layer 12 are formed by printing and the like method on the top face of lower board 2, and outer peripheries of upper board 1 and lower 2 are bonded together. During this process, at the edges of upper board 1 and lower board 2 where these gaps exist, plural openings are formed that communicate the gaps between upper conductive layer 3 and lower conductive layer 4 to the air.
As a result, when the top face of upper board 1 is pressed, air goes in and out through these gaps and openings. Sometimes, dusts or moisture attach to upper conductive layer 3 or to lower conductive layer 4 thus making electrical on-off action unstable. Furthermore, depending on the atmospheric pressure of the environment of the use of the touch panel, swelling or depression of upper board 1 may be caused, further causing interference fringes, the so-called Newton rings, due to reflection of external light and making displayed information on the display device behind the touch panel difficult to read.
Accordingly, in order to prevent these inconveniences and ensure reliable electrical on-off action and good visibility, the following is generally practiced at the expense of extra work. Namely, an adhesive is applied to these gaps and openings after bonding upper board 1 and lower board 2 together, and the air space between upper conductive layer 3 and lower conductive layer 4 is sealed.
As related art information of the invention of this application, Japanese Unexamined Patent Application Publication No. 2003-58319 is known.
As discussed above, conventional touch panels disadvantageously require sealing of plural gaps and openings with an adhesive in order to maintain insulation between electrodes and dummy patterns, costing time for fabrication and resulting in a higher cost.